Conventionally, there are a number of types of, for example, digital still cameras, and one of the types is a compact type for which a zoom lens with higher magnification power and higher imaging ability is sought.
There are a number of three-unit zoom lenses that have been proposed as zoom lenses suitable for the compact type, and the three-unit zoom lenses includes, in order from an object side, a first lens unit having negative optical power, a second lens unit having positive optical power, and a third lens unit having positive optical power. For a magnification change ratio of up to three times, these three-unit zoom lenses can be configured to be compact and have a wide field view at a wide-angle end. However, it is not possible to obtain a high magnification power zoom lens because an F-number at a telephoto end is large compared with an F-number at the wide-angle end.
As zoom lenses which ensure relatively high magnification power without the F-number at the telephoto end being significantly large compared with the F-number at the wide-angle end, there have been proposed a number of four-unit zoom lenses, as described in, for example, Japanese Laid-Open Patent Publication Nos. 2001-13411, 2001-42215, 2002-72087, and 2002-196241, including, in order from an object side, a first lens unit having a positive refractive optical power, a second lens unit having a negative refractive optical power, a third lens unit having a positive refractive optical power, and a fourth lens unit having a positive refractive optical power.